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1 | Network priority cgroup | ||
2 | ------------------------- | ||
3 | |||
4 | The Network priority cgroup provides an interface to allow an administrator to | ||
5 | dynamically set the priority of network traffic generated by various | ||
6 | applications | ||
7 | |||
8 | Nominally, an application would set the priority of its traffic via the | ||
9 | SO_PRIORITY socket option. This however, is not always possible because: | ||
10 | |||
11 | 1) The application may not have been coded to set this value | ||
12 | 2) The priority of application traffic is often a site-specific administrative | ||
13 | decision rather than an application defined one. | ||
14 | |||
15 | This cgroup allows an administrator to assign a process to a group which defines | ||
16 | the priority of egress traffic on a given interface. Network priority groups can | ||
17 | be created by first mounting the cgroup filesystem. | ||
18 | |||
19 | # mount -t cgroup -onet_prio none /sys/fs/cgroup/net_prio | ||
20 | |||
21 | With the above step, the initial group acting as the parent accounting group | ||
22 | becomes visible at '/sys/fs/cgroup/net_prio'. This group includes all tasks in | ||
23 | the system. '/sys/fs/cgroup/net_prio/tasks' lists the tasks in this cgroup. | ||
24 | |||
25 | Each net_prio cgroup contains two files that are subsystem specific | ||
26 | |||
27 | net_prio.prioidx | ||
28 | This file is read-only, and is simply informative. It contains a unique integer | ||
29 | value that the kernel uses as an internal representation of this cgroup. | ||
30 | |||
31 | net_prio.ifpriomap | ||
32 | This file contains a map of the priorities assigned to traffic originating from | ||
33 | processes in this group and egressing the system on various interfaces. It | ||
34 | contains a list of tuples in the form <ifname priority>. Contents of this file | ||
35 | can be modified by echoing a string into the file using the same tuple format. | ||
36 | for example: | ||
37 | |||
38 | echo "eth0 5" > /sys/fs/cgroups/net_prio/iscsi/net_prio.ifpriomap | ||
39 | |||
40 | This command would force any traffic originating from processes belonging to the | ||
41 | iscsi net_prio cgroup and egressing on interface eth0 to have the priority of | ||
42 | said traffic set to the value 5. The parent accounting group also has a | ||
43 | writeable 'net_prio.ifpriomap' file that can be used to set a system default | ||
44 | priority. | ||
45 | |||
46 | Priorities are set immediately prior to queueing a frame to the device | ||
47 | queueing discipline (qdisc) so priorities will be assigned prior to the hardware | ||
48 | queue selection being made. | ||
49 | |||
50 | One usage for the net_prio cgroup is with mqprio qdisc allowing application | ||
51 | traffic to be steered to hardware/driver based traffic classes. These mappings | ||
52 | can then be managed by administrators or other networking protocols such as | ||
53 | DCBX. | ||
54 | |||
55 | A new net_prio cgroup inherits the parent's configuration. | ||